Method for making a rotary piston internal combustion engine

ABSTRACT

A rotary piston machine, comprising a housing and a cylinder in said housing, has a piston provided with a number of apexes planetarily moving and rotating within said cylinder. Each apex carries in a groove a sealing strip for engagement with the cylinder wall of said housing. This cylinder wall is formed as the envelope surface generated by a worn sliding surface of said sealing strip. Said sliding surface has in turn been formed through wearing it off in a rotary piston machine during the operation of said machine. During its generating movement and while the piston is planetary moved the worn sliding surface has a fixed distance from the centre axis of the rotor.

United States Patent [1 1 Seidl [451 Oct.7,1975

[ METHOD FOR MAKING A ROTARY PISTON INTERNAL COMBUSTION ENGINE Related US. Application Data [62] Division of Ser. No. 255,573, May 22, 1972,

abandoned.

[30] Foreign Application Priority Data June 7, 1971 Sweden 7310/71 [52] US. Cl 29/1564 R; 418/178; 123/8.01; 5l/DIG. 32

[51] Int. Cl. B231 15/00 [58] Field of Search 418/178, 122-124, 418/113; l23/8.01; 29/l56.4 R; 51/DIG. 32;

[56] References Cited UNITED STATES PATENTS 3,102,492 9/1963 Bentele et a1 418/122 3,193,189 7/1965 Rastogi 418/122 3,196,848 7/1965 Bensinger 3,226,013 12/1965 Toyoda et a1 418/122 FOREIGN PATENTS OR APPLICATIONS 957,922 5/1964 United Kingdom 5l/D1G. 32

Primary Examiner-C. W. Lanham Assistant Examiner-Dan C. Crane Attorney, Agent, or Firm-Young & Thompson [5 7] ABSTRACT A rotary piston machine, comprising a housing and a cylinder in said housing, has a piston provided with a number of apexes planetarily moving and rotating within said cylinder. Each apex carries in a groove a sealing strip for engagement with the cylinder wall of said housing. This cylinder wall is formed as the envelope surface generated by a worn sliding surface of said sealing strip Said sliding surface has in turn been formed through wearing it off in a rotary piston machine during the operation of said machine. During its generating movement and while the piston is planetary moved the worn sliding surface has a fixed distance from the centre axis of the rotor.

2 Claims, 3 Drawing Figures Sheet 1 0f 2 3,99,897

U. Patent 0m. 7,1975

UM Pamnt (M11975 Sheet 2 01 2 3,,897

METHOD FOR MAKING A ROTARY PISTON INTERNAL COMBUSTION ENGINE This is a division, of application Ser. No. 255,573, filed May 22, 1972, now abandoned.

The present invention relates to a rotary machine and more particularly to a rotary piston internal combustion engine, comprising a housing and a cylinder in said housing, a piston planetarily moving and rotating within said cylinder, said piston being provided with a plurality of apex portions extending axially and each having a sealing strip for engagement with the cylinder wall of said housing.

The cylinder wall of previously known rotary piston machines has usually the shape of the outer curve parallel to an n-lobed, preferably 2-lobed epitrochoid, while the apex sealing strips have their sliding surfaces in the shape of the inner envelope of the cylinder wall that is, have continuous sliding contact with that Wall upon rotation of the piston without moving relative to the piston.

The object of this geometrical arrangement is to ensure the permanent sealing engagement between the apex sealing strips and the cylinder wall without any radial movement of the sealing strips in their grooves in the piston apexes.

However, this arrangement works perfectly only when the machine is new and when the sliding surfaces of the sealing strips are not worn off. The sealing strips are subjected to a very complicated loading under the operating conditions. The inclination of the sealing strip to the instantaneous normal of the inner surface of the cylinder wall varies during a revolution of the piston, the sealing strip is variably thermally stressed and it is influenced by the variable gas pressure in radial as well as in axial directions. All these influences together lead to an unequal wear of the sliding surface of the sealing strip, so that its simple circular shape changes into a very complicated curve after some time of operation. Thus the basic geometrical arrangement is spoiled and the permanent sealing engagement between the sealing strips and the cylinder wall is maintained only at the price of a radial movement of the sealing strips in their apex grooves. However, this has an unfavourable effect on the sealing strip itself as well as on the function of the whole machine. The radial movements forced upon the sealing strip can initiate inertial forces so large that the sealing strip can start to jump off from the cylinder wall expecially at high speeds of the machine and when the sealing strip is heavy. Due to the inertial forces the sealing strip can start vibrating which may lead to a quick wear of its sliding surface as well as to the damage of the cylinder wall by the well known chatter marks". The radial movement of the sealing strip, its eventual jumping off and its vibration cause an excessive stress on the spring used to keep the sealing strip in engagement with the cylinder wall, the spring thereby being fatigued and eventually even being fractured.

The object of the present invention is to eliminate or at least to reduce the disadvantages mentioned above. According to the present invention the curve of the cylinder wall has the shape of the envelope surface generated by a sliding surface of the sealing strip, and sliding surface being formed through wearing it off in a rotary piston machine during the operation of said machine, said sliding surface further during its generating movement and while the piston is planetarily moved having a fixed distance from the centre axis of the piston.

Other objects and advantages of the present invention will become apparent from a consideration of the following description taken in connection with the accompanying drawings, in which:

FIG. 1 is a transverse sectional elevation of a planetary piston internal combustion engine FIG. 2 is an enlarged fragmentary sectional view of the cylinder wall and one of the apexes of the piston;

FIG. 3 is a diagrammatic representation of the production of a pattern with a slotting tool.

In the drawing 1 is the stationary housing having a cavity 2, the outer limitation of which is the cylinder wall 8 having a 2-lobed shape. In said cavity 2 rotates a planetary piston 3 provided with three apexes, said piston 3 being mounted for rotation on an excentric portion 4 of a rotatable shaft. 5. Sealing strips 6 being a part of the sealing system are carried in grooves 7, extending in the length direction of the apexes. These strips are pressed against the cylinder wall 8 by means of a spring 9. Hereby is ensured a permanent sealing engagement between the sealing strip 6 and the cylinder wall during the planetary rotation of the piston.

This planetary movement is effected through the rotation of the piston 3 in a circle having the radius e at an angular speed w and further through the rotation of the piston 3 in the same direction around its own shaft 4 at an angular speed (0/3.

The sliding surface of the apex sealing strip 6, which is in sealing engagement with. the cylinder wall 8, has the shape formed by the wear of this surface during the operation of the engine. In FIG. 2 this sliding surface has been designated 10. In the same FIG. 2 is also shown as a comparison the original shape of the sliding surface of such a sealing strip, which sliding surface is designated 11 and is the inner envelope to a curve 12 parallel to the epitrochoid.

The shape of the worn sliding surface is very complicated and it is difficult to define it mathematically, because it is formed under the influence of complicated operating conditions. The surface is different in different types of rotary piston machines, it varies with the various ratios of the eccentricity e to the distance of the sliding surface from the centre axis of the rotor. It is influenced by different material in the sealing strip and in the housing and by several other conditions.

This complicated shape of the sliding surface 10, which is formed by the real wear during real operating conditions, is the basis of the geometrical arrangement of the rotary piston machine according to the invention, as the shape of the cylinder wall 8 is based on this sliding surface 10 and shaped as the envelope surface of this sliding surface 10.

The cylinder wall 8 of the housing 1 is usually very hard and wear-proof, while the sealing strip 6 is usually softer and is worn off more quickly. The cylinder wall 8 of the housing 1 will keep its shape as envelope surface to the sliding surface 10 through the whole normal life of the machine, as its wear is negligible. The sliding surface of the sealing strip 6, after a running-in period, will be worn offin such a way that the sliding curves 10 formed in various stages of the operating period will be approximately parallel to each other.

As a result the correct geometrical arrangement of the rotary piston machine will be maintained during the whole life time or at least will be maintained better than in the known machines. It means that the sealing strip will keep its permanent sealing engagement with the cylinder wall 8 without any real radial movement in the apex groove 7 of the piston 3.

In practice the cylinder wall 8 is shaped in the following way. The shape of the sliding surface 10 is transferred from the worn strip 6 bycopying to a slotting tool. This slotting tool together with a suitable machine tool serves for making the pattern. If the slotting tool and the pattern rotate around parallel axes in the same direction, the angular speed of the pattern being to and the angular speed of the slotting tool being %(u, then the slotting tool will make the 2-lobed curve in the pattern. If another ratio of angular speeds is set there will be another number of lobes in the pattern. The shape of the cylinder wall will be made by copying from the pattern.

FIG. 3 shows the method of making a pattern 7 by means of a slotting tool 13. From the above discussion of the method, it will be clear that a sealing strip having a worn sliding surface is removed from the ordinary piston of an ordinary rotary piston engine which is not improved according to the present invention, having a 2- lobed epitrochodial cylinder wall in which a 3-apex piston has been operated with rotational and planetary movement. The worn slotting surface of this sealing strip removed from the used engine, is copied onto the slotting tool 13 for the purpose of producing the pattern 17. Tool .13 is then inserted in a dummy piston 14 rotating about an axis 15. Piston 14 with tool 13 has a rotational path identical to that of an actual piston and its sealing strip, in the direction of the arrow 16, and will, like the engine it is to help produce, rotate with an annular speed of w, 00 being the angular speed of a pattern disc 17 which rotates about an axis 18 parallel to axis and spaced from axis 15 the same distance e as in FIG. 1, in the direction of the arrow 19 in FIG. 3. The tool 13 thus cuts a 2-Iobed curvature 20 in the pattern disc 17. This curvature 20 is then reproduced on an actual cylinder wall; while the curvature of slotting tool 13, that is, of the worn. sealing strip, is preferably reproduced on the new sealing strips that will contact that new cylinder wall.

It is possible to make the sliding surface of a new sealing strip 6 according to the curve 10. In that case this strip will not move radially in the groove 7 already at the beginning of the operating period.

It is however advantageous in some cases to make the sliding surface of the strip 6 in a simply rounded form, the radius thereby being so selected that the rounded sliding surface approaches to the sliding surface 10 as much as possible. In that case the basic geometrical arrangement of the rotary piston machine according to the invention is not so perfect during the running-in period, which means that the sealing strip 6 then will move radially in the groove 7 during this period, but after running-in, when the sliding surface of the strip 6 will get the worn shape, the radial movement will stop.

The cylinder wall of the housing according to the invention is advantageous also for other types of rotary piston machines than is shown in FIGS. 1 and 2, e.g. for rotary piston machines having a stationary housing with a 3-lobed cylinder wall and a 4-apexed piston or for rotary piston machines having a rotary housing with an n-lobed cylinder wall and a piston with n+1 apexes, both these parts rotating around parallel axes in the same direction and at different angular speeds.

Having described my invention, I claim:

1. A method of making a rotary piston internal combustion engine comprising a housing and a cylinder in said housing, a piston planetarily moving and rotating within said cylinder and having a plurality of apex portions extending parallel to the axis of the piston and each having a sealing strip with a sliding surface for engage ment with a cylinder wall of said housing, said method comprising taking a sealing strip with a worn.

sliding surface from a used rotary piston engine having an n-lobed epitrochoidal cylinder wall in which an n 1 apexed used piston is mounted for rotational and planetary movement, copying the curvature of said worn sliding surface onto a pattern-producing tool and producing a pattern of a cylinder wall curvature by moving said tool in a rotational path identical to that of said used piston, and thereafter copying said pattern to produce a new cylinder wall curvature which is the envelope of said worn sliding surface.

2. A method as claimed in claim 1, and shaping the sliding surface of new sealing strips to be used with the new curvature cylinder wall to the curvature of said worn sealing strip sliding surface before installing said new strips in a new piston, and thereafter introducing said new piston and sealing strips in a housing having said new curvature cylinder wall. 

1. A method of making a rotary piston internal combustion engine comprising a housing and a cylinder in said housing, a piston planetarily moving and rotating within said cylinder and having a plurality of apex portions extending parallel to the axis of the piston and each having a sealing strip with a sliding surface for engagement with a cylinder wall of said housing, said method comprising taking a sealing strip with a worn sliding surface from a used rotary piston engine having an n-lobed epitrochoidal cylinder wall in which an n + 1 apexed used piston is mounted for rotational and planetary movement, copying the curvature of said worn sliding surface onto a pattern-producing tool and producing a pattern of a cylinder wall curvature by moving said tool in a rotational path identical to that of said used piston, and thereafter copying said pattern to produce a new cylinder wall curvature which is the envelope of said worn sliding surface.
 2. A method as claimed in claim 1, and shaping the sliding surface of new sealing strips to be used with the new curvature cylinder wall to the curvature of said worn sealing strip sliding surface before installing said new strips in a new piston, and thereafter introducing said new piston and sealing strips in a housing having said new curvature cylinder wall. 